Field of the Invention
The present invention relates generally to methods for measuring the thickness of articles prepared from composite materials, and methods for correcting variations in thickness.
Description of Related Art
Airplane manufacturers are under increasing pressure to produce aircraft that are lightweight, strong, and durable at the lowest possible manufacturing cost and lifecycle maintenance. Airplanes and helicopters must have sufficient structural strength to withstand stresses during flight, while at the same time being as light as possible to maximize aircraft performance. To address these concerns, aircraft manufacturers have increasingly turned to composite materials. These composite materials, such as for example, fiber-reinforced resin matrix composites, provide improved strength, fatigue resistance, stiffness, and strength-to-weight ratio by incorporating carbon fibers into a softer, more ductile resin matrix.
Composite materials typically make up a major portion of military aircraft today, frequently making up 40% or more in terms of the structural mass, and typically covering 80% or more of the aircraft surfaces. The processing conditions and the installation of the composite material panels or skins onto a frame may result in variations in the thickness of adjoining parts. Additionally, during general preparation of composite material panels using traditional lay-up mandrel procedures, variations in the thickness of the parts may also occur. Manufacturers seek to minimize the variation between adjoining parts, particularly in critical areas, such as, on the wings of the aircraft.
Prior art methods for correcting variations in the thickness of adjoining skins typically involved the application of sacrificial plies of a composite part, for example, a composite prepreg tape material across the joint between adjoining parts. Post cure machining of the sacrificial plies by either grinding or sanding is frequently required to reduce the thickness to predetermined thickness threshold requirements for specific parts. However, the extent of machining necessary typically cannot be determined until final assembly of the aircraft. Additionally, the precision milling machines required for the post cure machining are typically very expensive and substantial time is required for the machining process. Furthermore, prior art methods for correcting for variations in thickness of the parts are often less precise. Thus, methods are needed for accurate identification of thickness variations and methods correction thereof.